1. Field of the Invention
The present invention relates generally to a device for separating particles based on particle density, and more particularly it relates to a foam separation device where the low density particles are supported on a bed of foam while the high density particles are able to penetrate the bed.
2. Description of the Prior Art
In food processing, it is often desirable to separate the edible and unedible portions of a food product. For example, in processing raisins, it is necessary to separate the fruit from a variety of waste materials including stems, leaves, dried vine, mold-damaged berries and the like. Various mechanical means have been devised to achieve such separation.
One approach employs the principle of film or froth flotation. Such methods rely on differences in the surface characteristics of particles to cause one group of particles to float while the remaining particles sink. Typically, surface active agents will be added to the flotation media to affect the surface wetability of the particles to aid in selecting which particles sink and which float. One such system is the Froth Flotation Cleaner manufactured by a Key Equipment Company/Electro-Sonic Control, Milton-Freewater, Oreg. Such system is described in U.S. Pat. No. 2,689,650. See also: U.S. Pat. No. 2,293,469, which describes a film flotation system employing a rotating drum for separating mineral ores.
A device intended primarily for separating raisins from waste material is described in U.S. Pat. No. 4,169,787 to one of the inventors herein. The system described therein relies on separating the raisins from the waste material using an upward flow of water or solution of adjusted specific gravity.
No method or device proposed heretofore has been entirely successful in separating raisins from associated waste materials. Froth or film flotation devices are not always able to distinguish between the raisins and the debris based on difference in surface properties. Moreover, conventional flotation devices require that the denser material, e.g., raisins, be periodically removed from the liquid separation media which renders it more difficult to perform a continuous separation. The device of U.S. Pat. No. 4,169,787, while achieving separation in a continuous manner, is relatively complex and expensive. It would therefore be desirable to provide a separator capable of accurately separating raisins from associated waste materials, on a continuous basis, which is both simple and relatively inexpensive.